Material for blackboards comprising synthetic resin and process for making the same

ABSTRACT

A composite material for blackboards essentially consisting of a layer of synthetic resin containing fine grains of an inorganic material distributed therein, said layer being deposited on a flexible carrier body and having a top coating of an antistatic agent. The composite material may be used as such or mounted on a stiff board. The invention also relates to a process for preparing the composite material which comprises the steps of mixing fine grains of inorganic material evenly into the synthetic resin, depositing the mixture on a flexible carrier and applying on top a coating of an antistatic agent.

United States Patent Kawaguchi 1 1 Feb. 15, 1972 [S4] MATERIAL FORBLACKBOARDS 2,541,497 2/1951 Buxbaum et a1 .35/66 COMPRISING SYNTHETICRESIN AND games ..1 17/1388 6 ennemann 1 r 1 ,.1 17/76 PROCESS FORMAKING THE SAME 2,955,364 10/1960 Shaw et a1 1 135/66 1 72] Inventor:Ryum Kawaguchi, Tokyo, Japan 3,497,969 3/1970 Schwoegler... 35/06 I3,515,626 1/1970 Duffield ....1o1/lb2 1 1 Aflwnecl WW Rubber Ltd-r3,525,664 8/1970 Hale et a1 17/28 x Tokyo. Japan [22] Filed: May 28,1969 Primary Examiner-William A, Powell pp No 828,475 Attorney-McGlewand Toren [57] ABSTRACT {30] Foreign Application Priority Data i Acomposite material for blackboards essentially consisting of Sept. 10,1968 Japan ..43/64832 a layer f th ti in containing fine grains of aninorganic material distributed therein, said layer being deposited on a[52] US. Cl ..161/88, 35/66, 117/28, flexible carrier body and having atop coating of an antistatic 117/76, 117/104, 117/1 19.2, 117/138.8,161/162, agent. The composite material may be used as such or 161/163,161/168, 161/171, 161/250 mountedonastiffboard. ll. 'r invention alsorelaws to a process for p p g he [58] Field 0' Search ..35/66; 161/88,162, I63, 168, posite material which comm-i565 the steps 0f mixing finegrains 161/1711 250; 1 17/27- 1333, 119-2 of inorganic material evenlyinto the synthetic resin, depositing the mixture on a flexible carrierand applying on top a [56] References Cited coating of an antistaticagent.

UNITED STATES PATENTS 9 Claims, 5 Drawing Figures 2,452,235 10/1948 Gold..35/66 PAIENIEBFEB 15 I972 3.642.562

sum 1 or 2 Ryuzo Kowoguchi ATTORNEY PAENIEDHB 15 1912 SHEET? 0P2 FIG.4

FIG.5

R H mm m N 0 m Aw w A Wu m WW MATERIAL FOR BLACKBOARDS COMPRISINGSYNTHETIC RESIN AND PROCESS FOR MAKING THE SAME SUMMARY OF THE INVENTIONThe present invention relates to a material for a blackboard and to aprocess of making the same.

The term "blackboard" is intended to designate any dark, smooth surfaceused for writing, drawing and the like with chalk or crayons.

More particularly, the invention relates to a blackboard made ofsynthetic resin with flne grains or inorganic material evenlydistributed in the resin and the mixture spread over a flexible carrierbody which may, if desired, be mounted on a rigid board. As a topcoating, the composite body comprises an antistatic agent for a purposeto be explained hereinbelow.

Attempts have already been made to use synthetic resins as surfacematerials for blackboards which were, however, not entirely satisfactoryfor the intended purpose. In order to understand this, it should beborne in mind that the ideal difference in brightness, measured by aconventional scale of brightness, between a new surface of a blackboardand one which was already used, should not exceed 2 or 3. In ablackboard, the surface of which consists substantially of syntheticresin, the difference is considerably greater because chalk particleswill stick to the surface of the blackboard due to static electricityproduced by friction between said surface and the chalk or eraser.

Such an increase in the difference of brightness between new and usedsurfaces causes writings or drawings to become indistinct. With abrightness difference of more than two or three, the blackboard becomespractically useless for the pur pose of writing or drawing thereon.

This is the main reason why blackboards with a surface consisting ofsynthetic resin have not been used up to now, in spite of the advantagesof low cost and high durability.

It is an object of the invention to provide material for blackboardswhich consist substantially of synthetic resin, but are free of theabove-mentioned drawback of the known blackboards.

It is another object of the invention to provide material forblackboards having a surface of synthetic resin which after use will nothave a difference in brightness as compared to the unused surfaceportions of more than 2 or 3.

It is yet another object of the invention to provide a process formaking blackboard material having the above advantageous properties.

Other objects and advantages of the invention will become apparent fromthe following detailed description, together with the accompanyingdrawing.

Generally speaking, the material according to the invention is composedof a layer of synthetic resin in which fine grains of an inorganicmaterial are evenly dispersed. This composite layer is deposited on aflexible carrier body and is coated on top with an antistatic agent. Thecomposite flexible sheet thus obtained may be used as such, that is tosay, it may either be used to cover a wall or it may be rolled into acylindrical sheet. a scroll-shaped sheet or map and the like.

In another embodiment, the composite sheet may be applied by means of anadhesive to a rigid base board such as veneer board, chipboard and thelike, to form a conventional blackboard.

In the accompanying drawings, the two embodiments mentioned above areillustrated by way ofexample.

FIG. I is a plan view of the composite flexible sheet. partly brokenaway;

FIG. 2 is a section taken along line 22 of FIG. 1;

FIG. 3 is a similar showing on a larger scale;

FIG. 4 illustrates the second embodiment in plan view; and

FIG. 5 is a section taken along line 5-5 of FIG. 4.

Referring to FIGS. I3 of the drawing, 1 designates a layer of asynthetic resin in which a plurality of grains 2 are evenly distributed.At 3, a carrier body is shown which consists of a flexible sheet, and 4designates an antistatic agent which forms the top coating.

In FIGS. 4 and 5, ll designates the layer of synthetic resin in whichgrains 12 are distributed. The flexible carrier body is shown at 13, theantistatic agent at [4. In this embodiment, a rigid base body is shownat 15, attached to the flexible carrier by a layer of adhesive I6.

The process for making the blackboard material of the inventioncomprises the steps of first mixing fine grains of inorganic materialinto a synthetic resin, evenly distributing the grains throughout theresin, thereafter applying the mixture onto a flexible sheet serving asa carrier and, finally, coating, e,g., spraying, the top of thecomposite material with an antistatic agent.

To make a rigid blackboard as conventionally used in schools, thecomposite material is mounted on a stiff board by means ofa knownadhesive. The mounting can be done before or after the application ofthe antistatic coating.

The materials to be used in the various steps and which will form theseveral layers of the composite body will now be described in fulldetail.

The synthetic resin may be thermoplastic or thermosetting or a mixtureof both types. Synthetic resins to be used individually or as a mixtureinclude: soft polyvinyl chloride, polyethylene, polypropylene,polyethylene-acetic acid copolymer, vinyl chloride-vinyl acetatecopolymer, acrylonitrile-butadiene-styrene copolymer, synthetic rubberunsaturated polyester resin, polyurethane elastomer, double fluidpolyurethane, epoxy resin and diallyl phthalate.

The fine grains or inorganic material to be distributed evenly in thesynthetic resin individually or as a mixture include: silica sand,glass, aqueous rock, quartz, silicon carbide, aluminum oxide, mica andiron oxide.

The flexible carrier may be formed by a sheet of synthetic resin,synthetic leather, paper or cloth.

The antistatic agent applied as top coating may be a product derivedfrom partial hydrolysis of silicon tetrachloride, a surface active agentof cation type or a surface active agent of amphoteric type. Theantistatic agent effectively prevents static electricity from developingclue to friction between chalk and blackboard surface or between eraserand blackboard surface, which would otherwise attract particles of chalkto the blackboard surface and thereby reduce the efflciency of theeraser.

Since the carrier is a flexible sheet, it may be easily applied to anybaseboard, especially to a curved baseboard. Furthermore, this featureof the invention is advantageous when entire walls ofa room, for examplea classroom, are to be used as surfaces on which writings or drawingswith chalk can be made and erased. To this end, the surface material ofthis invention may be applied to walls by use of an adhesive.

When the flexible sheet is to be applied to a base board, such aschipboard or other hard board, to make a conventional blackboard, anyadhesive may be employed that will join the resin sheet to the board.Many adhesives are known which are derived from synthetic resins, phenolformaldehyde vinyl resins and others which may be conveniently used.

The synthetic resins to be used for the distribution of grains ofinorganic materials may be applied in various forms, e.g., as solutionsin organic solvents, pastes obtained by dispersing synthetic resin in aplasticizer which is soluble in the synthetic resin or in solid form.The form in which the resins are processed depends in each case on theequipment of the manufacture or on the availability of the resins in aparticular form.

The grains of inorganic material to be incorporated in the syntheticresin should be selected with a view to their hardness compared to thatof chalk. The main purpose of the grains is their counteracting theabrasion effected by the chalk. If the grains are of lower hardness thanchalk, they would not effectively prevent abrasion of the resin so thatthe blackboard would be worn away too soon.

The grain size has likewise some bearing on the usefulness of theblackboard. In any particular case, the size or diameter of the grainsdepends mainly upon the constituents of the chalk or crayons used andthe thickness of the coating of the resin surface layer; it may also beaffected by some factors of the preparation of the board.

When, for instance, the thickness of the antistatic coating is from50-100 microns, the grain diameter advantageously ranges from [-40microns. When the coating thickness is over I00 microns, larger grainsmay be used. In some cases, for instance when the coated blackboard isto undergo an embossing treatment or similar surface treatment, grainsof still larger diameter may be advisable.

It should be noted that the application of the antistatic agent is themost essential feature of the present invention since, without the same,many particles of chalk would remain after the erasing and the attemptedimprovement relating to difference in the brightness after use would notbe accomplished.

In the following examples, preferred embodiments of the invention willbe described by way of illustration, but it should be noted that manyvariations in the details can be made without departing from the spiritofthe invention.

All parts are by weight.

(EXAMPLE I l. A flexible sheet serving as carrier is made bycalandering, in a known manner, a mixture of Polyvinyl chloride resin (F800) I00 parts Dil lcthylhcxyhphthalatc 50 parts Whllt. lead 6 partsLead slcaratc l part Calcium carbonate 200 parts Pigmunl [dark green! 3parts into a sheet of 0.6 mm. thickness. This sheet resembles artificialleather.

2. The sheet of the synthetic resin consists primarily of polyurethanewith several additives. It is composed as follows:

A '4 \ulutmn of polyurethane in ethyl The solution 2 and the suspension3 are mixed thoroughly and spread on the flexible sheet described underl. The distribution of the mixture on the leather may be effected byspraying. The amount ofthe resin mixture is 300g./m.

The leather thus covered with the synthetic resin is then subjected toheat curing for 5 minutes in a furnace heated to l C. it is then allowedto cool and is rolled up, whereupon it is allowed to remain for about 48hours in a room in which the temperature is maintained constant at C.and the humidity at 55 percent. The curing of the product is therebyaccomplished.

Next, the product is placed on a flat support and coated with theantistatic agent by means of a roll-coater of the photogravure type. Theantistatic agent consists ofa 5 percent dispersion of the partiallyhydrolyzed product of silicon tetrachloride (trade name coalcoat, madeby the Coalcoat C0,, Ltd. of Japan) in a methanol-butanol mixture 2:1.The amount of the coating applied is gJm. The article is then dried for3 minutes in a furnace heated to 80 C., whereupon it is cooled androlled up once more.

The product thus obtained is ready for practical use as a scroll-shapedblackboard. In this embodiment. the brightness difference between a newsurface and an already used surface is 1.5 with the result that theeffect of erasions as well as distinctness of writings or drawings areof almost optimum quality.

EXAMPLE 2 The procedure of example I is followed until the flexibleleather sheet covered with the synthetic resin and topped by theantistatic agent is completely finished. The scrollshaped sheet is thenapplied to a plywood board having a thickness of 6 mm. withinterposition of adhesive material consisting of a vinyl acetateemulsion. The board is then allowed to stand for hours to permit theadhesive to set, whereupon the article is ready for use.

What is claimed is:

l. A composite material for blackboards which comprises a layer of asynthetic resin, said layer containing evenly distributed therein finegrains of an inorganic material, a flexible carrier body for said layerof synthetic resin, and a top coating of an antistatic agent derived bypartial hydrolysis of silicon tetrachloride.

2. The composite material according to claim 1, comprising as syntheticresin soft polyvinyl chloride, polyethylene, polypropylene,polyethylene-acetic acid copolymer, vinyl chloridewinyl acetatecopolymer, acrylonitrile-butadienestyrene copolymer, synthetic rubber,unsaturated polyester resin, polyurethane elastomer, double fluidpolyurethane, epoxy resin and diallyl phthalate, or a mixture of saidresins.

3. The composite material according to claim 1, comprising as inorganicmaterial grains of silica sand, glass, aqueous rock, quartz, siliconcarbide, aluminum oxide, mica or iron oxide, or mixtures thereof.

4. The composite material according to claim I, comprising as flexiblecarrier body a sheet of synthetic resin, synthetic leather, paper orcloth.

5. The composite material according to claim 1, comprising as anantistatic agent a surface active agent of cation type or of amphoterictype.

6. The composite material according to claim 1, wherein the grain sizeof the inorganic material has a diameter of l0-40 microns, dependent onthe hardness of the writing material used and on the coating thicknessof the antistatic agent.

7. A blackboard comprising a rigid base board and a body of compositematerial as claimed in claim I permanently affixed thereto.

8. A process for making composite materials for blackboards, whichcomprises incorporating into a synthetic resin fine grains of aninorganic material, thoroughly mixing the mass, depositing the same on aflexible carrier body, evenly spreading the synthetic on said carrier,and applying an antistatic agent derived by a partial hydrolysis ofsilicon tetrachloride as top coating on said composite material.

9. A process for making composite materials for blackboards, whichcomprises incorporating into a synthetic resin fine grains of aninorganic material, thoroughly mixing the mass, depositing the same on aflexible carrier body, evenly spreading the synthetic on said carrier,and applying an antistatic agent derived by a partial hydrolysis ofsilicon tetrachloride as top coating on said composite material andwhich comprises:

a. preparing a solution of polyurethane in ethyl acetatetoluene, addinga curing agent for the polyurethane and a thinner;

b. preparing, separately, a dispersion of silica sand powder, with agrain diameter of 25-40 microns, in butyl acetatetoluene;

c. mixing the solution and the dispersion;

spraying the combined mixture on a flexible sheet of synthetic resin inthe amount of about 300 g./m, and subjecting to curing for 5 minutes atC;

e. cooling the product, rolling it up and allowing it to remain for 48hours in a room with a temperature maintained at 25 C. and a humiditymaintained at 55 percent;

amount ofcoating applied being 30 gJm; and

g. drying the product for 3 minutes at rolling it up once more.

C.. cooling and

2. The composite material according to claim 1, comprising as syntheticresin soft polyvinyl chloride, polyethylene, polypropylene,polyethylene-acetic acid copolymer, vinyl chloride-vinyl acetatecopolymer, acrylonitrile-butadiene-styrene copolymer, synthetic rubber,unsaturated polyester resin, polyurethane elastomer, double fluidpolyurethane, epoxy resin and diallyl phthalate, or a mixture of saidresins.
 3. The composite material according to claim 1, comprising asinorganic material grains of silica sand, glass, aqueous rock, quartz,silicon carbide, aluminum oxide, mica or iron oxide, or mixturesthereof.
 4. The composite material according to claim 1, comprising asflexible carrier body a sheet of synthetic resin, synthetic leather,paper or cloth.
 5. The composite material according to claim 1,comprising as an antistatic agent a surface active agent of cation typeor of amphoteric type.
 6. The composite material according to claim 1,wherein the grain size of the inorganic material has a diameter of 10-40microns, dependent on the hardness of the writing material used and onthe coating thickness of the antistatic agent.
 7. A blackboardcomprising a rigid base board and a body of composite material asclaimed in claim 1 permanently affixed thereto.
 8. A process for makingcomposite materials for blackboards, which comprises incorporating intoa synthetic resin fine grains of an inorganic material, thoroughlymixing the mass, depositing the same on a flexible carrier body, evenlyspreading the synthetic on said carrier, and applying an antistaticagent derived by a partial hydrolysis of silicon tetrachloride as topcoating on saId composite material.
 9. A process for making compositematerials for blackboards, which comprises incorporating into asynthetic resin fine grains of an inorganic material, thoroughly mixingthe mass, depositing the same on a flexible carrier body, evenlyspreading the synthetic on said carrier, and applying an antistaticagent derived by a partial hydrolysis of silicon tetrachloride as topcoating on said composite material and which comprises: a. preparing asolution of polyurethane in ethyl acetate-toluene, adding a curing agentfor the polyurethane and a thinner; b. preparing, separately, adispersion of silica sand powder, with a grain diameter of 25-40microns, in butyl acetate-toluene; c. mixing the solution and thedispersion; spraying the combined mixture on a flexible sheet ofsynthetic resin in the amount of about 300 g./m2, and subjecting tocuring for 5 minutes at 120* C; e. cooling the product, rolling it upand allowing it to remain for 48 hours in a room with a temperaturemaintained at 25* C. and a humidity maintained at 55 percent; f.flattening the rolled product on a support and coating it with a 5percent solution of partially hydrolyzed solution tetrachloride inmethanol-butanol mixture 2:1, the amount of coating applied being 30g./m2; and g. drying the product for 3 minutes at 80* C., cooling androlling it up once more.